1. Field of the Invention
The present invention relates to a magnetic resonance imaging apparatus and magnetic resonance imaging method that uses a plurality of element coils to transmit an RF (radio frequency) pulse or receive a magnetic resonance signal.
2. Description of the Related Art
A magnetic resonance imaging apparatus in recent years can utilize various kinds of radio-frequency coils meeting the purposes. As such radio-frequency coils, there is one in which a plurality of element coils are arranged. Further, a plurality of types of radio-frequency coils may be simultaneously disposed in some cases.
Thus, in the magnetic resonance imaging apparatus, a plurality of element coils arranged in a radio-frequency coil or a plurality of types of radio-frequency coils can be connected in parallel, and the number of these coils is increasing.
On the other hand, all element coils connected in parallel in this manner are not simultaneously used. Therefore, the number of receiving circuits that receive magnetic resonance signals through element coils or the number of transmitting circuits that transmit RF pulses is smaller than the number of connectable element coils.
In such a case, element coils which should be used must be selectively connected with the receiving circuit or the transmitting circuit. However, the number of combinations of connection states is large, and hence a selecting circuit becomes very complicated. As the selecting circuit, a transfer type switch or a matrix switch is typically applied.
FIG. 14 is a view showing a structural example of a transfer type switch. In this example, four two-input/one-output selectors 141, 142, 143, and 144 constitute a four-input/two-output signal selecting circuit.
FIG. 15 is a view showing a structure of a 16-input/16-output matrix switch.
In the transfer type switch, a degree of flexibility in selection is small, and realization of multichannel is difficult.
In the matrix switch, a degree of flexibility in selection is higher than that in the transfer type, and realization of multichannel is relatively easy. However, in a multichannel type matrix switch, such an unconnected line called a stab as shown in FIG. 15 becomes long depending on a signal selection state. In case of a radio-frequency signal like a magnetic resonance signal, the signal may be degraded when a stab becomes long. Further, when the stab is long at the time of selecting an RF transmission signal, unnecessary radiation may be disadvantageously increased.
It is to be noted that, as a related technology, a technology disclosed in, e.g., JP-A 2001-46356 (KOKAI) is known.